Camera filter frame and camera filter unit

ABSTRACT

A camera filter unit (10) includes a front ring (4) for holding a polarization filter (2) and a rear ring (5) for rotatably holding the front ring (4). The front ring (4) includes a rear annular wall portion (18) extending in a radial direction (R), a rear annular plate portion (19) extending rearward from the inner peripheral end of the rear annular wall portion (18), and an annular projection portion (20) projecting for a short distance from the rear end of the rear annular plate portion (19) toward the outer peripheral side. The rear annular wall portion (18), the rear annular plate portion (19), and the annular projection portion (20) form an annular recess (21) on the outer peripheral surface of the front ring (4). The rear ring (5) includes an annular protrusion (45) protruding to the inner peripheral side. The annular protrusion (45) is inserted into the annular recess (21) of the front ring (4).

This application is a divisional of Patent Application No. 14/917,355filed on Mar. 8, 2016, which is National Stage Application ofInternational Application No. PCT/JP2014/074316, filed on Sep. 12, 2014,the disclosure of which is incorporated herein by reference in itsentirety. The International Application No. PCT/JP2014/074316 isentitled to and claims benefit of Japanese Patent Application No.2013-190529, filed on Sep. 13, 2013, the disclosures of which areincorporated herein by reference in their entireties.

FIELD

The present invention relates to a camera filter frame in which a frontring for holding an optical element is rotatably held by a rear ring.The present invention also relates to a camera filter unit in which thecamera filter frame holds an optical element such as a polarizationfilter.

BACKGROUND

A camera filter frame for holding a polarization filter is disclosed inPatent Literature 1. The camera filter frame of Patent Literature 1includes a front ring for holding the polarization filter and a rearring for holding the front ring. The front ring includes an annularrecess that is recessed to the inner peripheral side on the outerperipheral surface of the front ring. The rear ring includes an annularrecess that is recessed to the outer peripheral side on the innerperipheral surface of the rear ring. The front ring and the rear ringare combined in such a manner that the respective annular recesses faceeach other in the radial direction, and a washer is inserted into anannular space formed by the annular recess of the front ring and theannular recess of the rear ring. The washer has its outer peripheralportion positioned in the annular recess of the rear ring and its innerperipheral portion positioned in the annular recess of the front ring.This structure enables the front ring and the rear ring to rotaterelatively to each other about the axis with the washer as a guide.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent Application Publication No.2005-301172

SUMMARY Technical Problem

In order to insert a washer into an annular space formed by the annularrecess of the front ring and the annular recess of the rear ring, aC-shaped washer is first placed in the annular recess provided to theouter peripheral surface of the front ring. Next, open ends of thewasher are brought closer to each other to reduce the outside diameterof the washer so as to combine the front ring and the rear ring. Theannular recess of the front ring and the annular recess of the rear ringare then caused to face each other. As a result, an annular space isformed between the front ring and the rear ring, and then the washer'sown shape restoring force separates the open ends from each other torestore the outside diameter of the washer. Consequently, the washer hasthe outer peripheral portion positioned in the annular recess of therear ring and the inner peripheral portion positioned in the annularrecess of the front ring.

A washer that expands and contracts in the radial direction is easy tobe distorted. It is also difficult to maintain the washer placed in theannular space in a position orthogonal to the axis of each ring.Therefore, in the structure in which the front ring and the rear ringare caused to rotate relatively to each other with the washer as aguide, the washer comes into contact with each ring at random, whichmight cause the front ring not to rotate smoothly relative to the rearring.

In view of the foregoing, an object of the present invention is toprovide a camera filter frame in which a rear ring rotatably holds afront ring for holding an optical element with a simple structure usingno washer. Another object of the present invention is to provide acamera filter unit in which the camera filter frame holds an opticalelement.

Solution to Problem

To achieve the above object, a camera filter frame according to thepresent invention includes a front ring that holds an optical element onthe inner peripheral side thereof and includes an annular recess on theouter peripheral surface thereof, and a rear ring that includes, on theinner peripheral surface thereof, an annular protrusion inserted intothe annular recess and that holds the front ring rotatably.

According to the present invention, the front ring can rotate about theaxis using the annular protrusion of the rear ring that is inserted intothe annular recess as a guide. Consequently, no washer needs to be usedto allow the rear ring to hold the front ring rotatably. In the case inwhich the front ring is rotated using the annular protrusion that isdisposed in the rear ring as a guide, the guide (annular protrusion)does not become distorted, nor does the position of the guide (annularprotrusion) change. The annular protrusion serving as a guide can beformed more accurately than a washer or the like that expands andcontracts in the radial direction. Furthermore, because no member suchas a washer is interposed between the front ring and the rear ring, thefront ring and the rear ring can be combined accurately. The front ringheld by the rear ring can therefore be rotated smoothly.

In the present invention, the front ring includes an annular wallportion extending in the radial direction, an annular plate portionextending rearward from the inner peripheral end of the annular wallportion, and an annular projection portion projecting for a shorterdistance than the annular wall portion from the rear end of the annularplate portion toward the outer peripheral side. The annular recess isformed by the annular wall portion, the annular plate portion, and theannular projection portion. A position of the annular protrusion isbetween the annular wall portion and the annular projection portion inthe fore-and-aft direction and the annular plate portion is bent to theouter peripheral side to displace the annular projection portion to theouter peripheral side and the state in which the annular protrusion isinserted into the annular recess is created. In other words, in thepresent invention, the front ring includes an annular wall portionextending in the radial direction, an annular plate portion extendingrearward from the inner peripheral end of the annular wall portion, andan annular projection portion projecting for a shorter distance than theannular wall portion from the rear end of the annular plate portiontoward the outer peripheral side. The annular recess is formed by theannular wall portion, the annular plate portion, and the annularprojection portion. The annular wall portion includes a bent portionthat is bent to the outer peripheral side. This structure facilitatescreating the state in which the annular protrusion of the rear ring isinserted into the annular recess of the front ring.

In the present invention, it is preferable that the annular plateportion include an annular groove on at least one of the innerperipheral surface and the outer peripheral surface thereof, and that aportion in which the annular groove is formed in the annular plateportion be bent to displace the annular projection portion to the outerperipheral side. In other words, it is preferable that the annular plateportion include an annular groove on at least one of the innerperipheral surface and the outer peripheral surface thereof, and that aportion in which the annular groove is formed in the annular plateportion be a bent portion that is bent to the outer peripheral side.Because the portion in which the annular groove is formed is thinnerthan other portions, the rear annular plate portion can be bentaccurately with relatively weak force by bending this thin portion.Consequently, annular projection portion can be displaced accurately.This can improve the accuracy of dimension between the annularprotrusion of the rear ring and the annular recess of the front ring,preventing the front ring from rattling on the rear ring. The front ringcan therefore be rotated smoothly.

In the present invention, the camera filter frame can include a frontstopper that restricts the forward movement of the optical element, anda rear stopper that restricts the rearward movement of the opticalelement. The front ring can include a holding portion for holding theoptical element in a position closer to the front side than the positionof the annular wall portion is, the front stopper can be attached to theinner peripheral surface of the front ring, and the rear stopper can bethe annular wall portion. This structure can restrict the back-and-forthmovement of the optical element that is held to the front ring.

In this case, the front ring preferably holds the optical elementbetween the front stopper and the rear stopper in a rotatable mannerabout the axis. In this manner, stress (pressure) to be placed on theoptical element can be reduced compared with the case in which theoptical element is held to the front ring in an unrotatable manner whilebeing gripped by the front stopper and the rear stopper from the frontand rear. Because distortion can be prevented from occurring in theoptical element with lower stress placed on the optical element, finerimages and videos can be obtained when, for example, images and videosthe resolution of which is many times higher than full high-definitionones are shot.

It is preferable that the rear ring include an annular portionpositioned on the outer peripheral side of the holding portion closer tothe front side than the annular protrusion is, and that the holdingportion include an adhesive injection hole passing therethrough in adirection intersecting the axis of the holding portion. In this manner,after the optical element is held to the holding portion, an adhesivecan be injected through the adhesive injection hole to fix the opticalelement to the front ring. Because the annular portion of the rear ringis positioned on the outer peripheral side of the holding portion, theadhesive injection hole is not exposed to the outer peripheral side evenin the case in which the adhesive injection hole is provided in theholding portion. Consequently, the adhesive injection hole does notimpair the appearance of the camera filter frame.

In the present invention, the camera filter frame can include an innerring that is inserted into the front ring, and a rear stopper thatrestricts the rearward movement of the optical element. The inner ringcan include an annular frame for holding the optical element from theouter peripheral side, and a front stopper that protrudes from the frontedge of the annular frame to the inner peripheral side to restrict theforward movement of the optical element. The front ring can hold theinner ring in a position closer to the front side than the position ofthe annular wall portion is, and the rear stopper can be the annularwall portion. This structure allows the front ring to hold the opticalelement via the inner ring. This structure can also restrict theback-and-forth movement of the optical element that is held to the frontring.

In this case, the front ring preferably holds the optical elementbetween the front stopper and the rear stopper in a rotatable mannerabout the axis. In this manner, stress (pressure) to be placed on theoptical element can be reduced compared with the case in which theoptical element is held to the front ring in an unrotatable manner whilebeing gripped by the front stopper and the rear stopper from the frontand rear. Because distortion can be prevented from occurring in theoptical element with lower stress placed on the optical element, finerimages and videos can be obtained when, for example, images and videosthe resolution of which is many times higher than full high-definitionones are shot.

The annular frame can include an adhesive injection hole passingtherethrough in a direction intersecting the axis of the annular frame.In this manner, after the optical element is held to the annular frame,an adhesive can be injected through the adhesive injection hole to fixthe optical element to the annular frame. Because the annular frame isheld on the inner side of the front ring, the adhesive injection hole isnot exposed to the outer peripheral side even in the case in which theadhesive injection hole is provided in the annular frame. Consequently,the adhesive injection hole does not impair the appearance of the camerafilter frame.

In the present invention, it is preferable that the rear ring include anexternal thread in the rear end of the outer peripheral surface thereof,and that the annular protrusion be disposed in a position overlappingthe external thread when seen from the radial direction. In this manner,the dimension of the camera filter frame can be reduced in thefore-and-aft direction (axial direction) compared with the case in whichthe annular protrusion is formed in a position different from that ofthe external thread in the axial direction.

In the present invention, the rear ring can hold a second opticalelement on the inner peripheral side thereof. Specifically, the camerafilter frame can hold a first optical element to the front ring and asecond optical element to the rear ring.

In the present invention, the camera filter frame can include a secondfront stopper that restricts the forward movement of the second opticalelement, and a second rear stopper that restricts the rearward movementof the second optical element. The rear ring can include a secondannular projection portion that projects to the inner peripheral sidecloser to the rear than the front ring does, and a rear holding portionfor holding the second optical element at the rear of the second annularprojection portion. The second front stopper can be the second annularprojection portion, and the second rear stopper can be attached to theinner peripheral surface of the rear ring. This structure can restrictthe back-and-forth movement of the second optical element that is heldto the rear ring.

In this case, the rear ring preferably holds the second optical elementbetween the second front stopper and the second rear stopper in arotatable manner about the axis. In this manner, stress (pressure) to beplaced on the second optical element can be reduced compared with thecase in which the second optical element is held to the rear ring in anunrotatable manner while being gripped by the second front stopper andthe second rear stopper from the front and rear. Because distortion canbe prevented from occurring in the second optical element with lowerstress placed on the second optical element, finer images and videos canbe obtained when, for example, images and videos the resolution of whichis many times higher than full high-definition ones are shot.

In the present invention, the camera filter frame can include a rearinner ring that is inserted into the rear ring, and a second frontstopper that restricts the forward movement of the second opticalelement. The rear ring can include a second annular projection portionthat projects to the inner peripheral side at the rear of the frontring. The rear inner ring can include a rear annular frame that ispositioned at the rear of the second annular projection portion and thatholds the second optical element from the outer peripheral side, and asecond rear stopper that projects from the rear annular frame to theinner peripheral side to restrict the rearward movement of the secondoptical element. The second front stopper can be the second annularprojection portion. This structure can restrict the back-and-forthmovement of the optical element that is held to the rear ring.

In this case, the rear ring preferably holds the second optical elementbetween the second front stopper and the second rear stopper in arotatable manner about the axis. In this manner, stress (pressure) to beplaced on the second optical element can be reduced compared with thecase in which the second optical element is held to the rear ring in anunrotatable manner while being gripped by the second front stopper andthe second rear stopper from the front and rear. Because distortion canbe prevented from occurring in the second optical element with lowerstress placed on the second optical element, finer images and videos canbe obtained when, for example, images and videos the resolution of whichis many times higher than full high-definition ones are shot.

A camera filter unit according to the present invention includes thecamera filter frame as described above and a polarization filter that isheld by the front ring as the optical element.

According to the present invention, the front ring for holding thepolarization filter can be rotated smoothly with respect to the rearring.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a camera filter unit according to afirst embodiment;

FIG. 2A is a longitudinal sectional view of the camera filter unitaccording to the first embodiment;

FIG. 2B is a partially enlarged sectional view of the camera filter unitaccording to the first embodiment;

FIGS. 3A, 3B and 3C are diagrams for describing an assembly method ofthe camera filter unit;

FIG. 4A is a longitudinal sectional view of the camera filter unitaccording to a second embodiment;

FIG. 4B is a partially enlarged sectional view of the camera filter unitaccording to a second embodiment;

FIG. 5A is a longitudinal sectional view of the camera filter unitaccording to a third embodiment;

FIG. 5B is a partially enlarged sectional view of the camera filter unitaccording to a third embodiment;

FIG. 6A is a longitudinal sectional view of the camera filter unitaccording to a fourth embodiment;

FIG. 6B is a partially enlarged sectional view of the camera filter unitaccording to a fourth embodiment;

FIG. 7A is a longitudinal sectional view of the camera filter unitaccording to a fifth embodiment; and

FIG. 7B is a partially enlarged sectional view of the camera filter unitaccording to a fifth embodiment.

DESCRIPTION OF EMBODIMENTS

The following describes a camera filter unit to which the presentinvention is applied with reference to the drawings.

First Embodiment

FIG. 1 is a perspective view of a camera filter unit according to afirst embodiment. FIG. 2A is a longitudinal sectional view of the camerafilter unit in FIG. 1. FIG. 2B is a partially enlarged sectional viewthereof. As illustrated in FIG. 1 and FIG. 2A, a camera filter unit 1according to the present embodiment includes a disc-like polarizationfilter (optical element) 2, an inner ring 3 for holding the polarizationfilter 2 coaxially, a front ring 4 for holding the inner ring 3coaxially from the outer peripheral side, and a rear ring 5 for holdingthe front ring 4 coaxially. The front ring 4 holds the polarizationfilter 2 via the inner ring 3. The rear ring 5 holds the front ring 4rotatably about an axis L. The inner ring 3, the front ring 4, and therear ring 5 constitute a camera filter frame 10. In the followingdescription, the direction of the inner ring 3, the front ring 4, andthe rear ring 5 along the axis L is assumed to be a fore-and-aftdirection X of the camera filter unit 1. In the fore-and-aft directionX, the side on which the front ring 4 is positioned is assumed to be thefront side (front X1), and the side on which the rear ring 5 ispositioned is assumed to be the rear side (rear X2).

The front ring 4 holds the inner ring 3 in a position where the innerring 3 is not exposed from the front end of the front ring 4. On theinner peripheral surface of the front ring 4, an internal thread 11 isprovided in a region of a certain width from the front edge toward therear X2. The exposed portion of the internal thread 11 that is exposedto the front side more than the inner ring 3 is a front mounting portionfor mounting a cap or a hood into the front of the camera filter unit 1.On the outer peripheral surface of the rear ring 5, an external thread12 is provided in a region of a certain width from the rear edge towardthe front X1. The external thread 12 is a rear mounting portion formounting the camera filter unit 1 into a lens-barrel of an imaging lensor a camera. The inner ring 3, the front ring 4, and the rear ring 5 areall formed of a metal base. In the present embodiment, the inner ring 3,the front ring 4, and the rear ring 5 are all made of aluminum.

(Front Ring)

As illustrated in FIG. 2B, the front ring 4 includes a front annularplate portion 15 extending in the fore-and-aft direction X along theaxis L, a front annular wall portion 16 extending from the rear end ofthe front annular plate portion 15 toward the inner peripheral side in aradial direction R orthogonal to the axis L, an intermediate annularplate portion 17 extending from the inner peripheral end of the frontannular wall portion 16 to the rear X2 along the axis L, a rear annularwall portion (annular wall portion) 18 extending from the rear end ofthe intermediate annular plate portion 17 toward the inner peripheralside in the radial direction R, a rear annular plate portion 19extending from the inner peripheral end of the rear annular wall portion18 to the rear X2, and an annular projection portion 20 projecting for ashorter distance than the rear annular wall portion 18 from the rear endof the rear annular plate portion 19 toward the outer peripheral side.On the outer peripheral surface of the front ring 4, an annular recess21 is formed by the rear annular wall portion 18, the rear annular plateportion 19, and the annular projection portion 20.

The front annular plate portion 15 includes a thick portion 23 and athin portion 24 in this order from the front X1 toward the rear X2. Thethick portion 23 projects to the outer peripheral side more than thethin portion 24 does. An annular step 25 is formed by the thick portion23 and the thin portion 24 on the outer peripheral surface of the frontannular plate portion 15. The internal thread 11 serving as a frontmounting portion is formed on the inner peripheral surface of the frontannular plate portion 15.

The front annular wall portion 16 has a constant thickness dimension inthe fore-and-aft direction X. The intermediate annular plate portion 17has a constant thickness in the radial direction R. The rear annularwall portion 18 has a constant thickness dimension in the fore-and-aftdirection X.

The rear annular plate portion 19 inclines to the outer peripheral sidetoward the rear X2. More specifically, the front end of the outerperipheral surface of the rear annular plate portion 19 (portionadjacent to the rear annular wall portion 18) is provided with anannular groove 27, and the portion in which the annular groove 27 isformed is bent to the outer peripheral side so that the rear annularplate portion 19 inclines to the outer peripheral side. Specifically, inthe rear annular plate portion 19, the portion in which the annulargroove 27 is formed is a bent portion that is bent to the outerperipheral side. The rear portion of the outer peripheral surface of therear annular plate portion 19 (portion adjacent to the annularprojection portion 20) is provided with an annular notch 28. The notch28 is shallower than the annular groove 27.

The annular projection portion 20 projects in a direction orthogonal tothe rear annular plate portion 19. Consequently, the annular projectionportion 20 extends to the front X1 toward the outer peripheral side. Inthe present embodiment, the annular projection portion 20 has atrapezoidal sectional shape tapering toward the tip. The innerperipheral portion of an annular protrusion 45 provided to the rear ring5 is inserted into the annular recess 21 formed by the rear annular wallportion 18, the rear annular plate portion 19, and the annularprojection portion 20.

(Inner Ring)

The inner ring 3 includes an annular frame 31 for holding thepolarization filter 2 coaxially from the outer peripheral side, and anannular front stopper 32 that projects from the front edge of theannular frame 31 to the inner peripheral side to restrict the movementof the polarization filter 2 to the front X1. The front stopper 32 isabuttable from the front X1 on the outer peripheral edge of thepolarization filter 2 that is held by the annular frame 31.

The inner peripheral surface of the annular frame 31 is an annularsurface that extends with a constant diameter dimension along the axisL, and is a filter holding surface 33 for holding the polarizationfilter 2 coaxially. The annular frame 31 includes a thick frame portion34 and a thin frame portion 35 in this order from the front X1 towardthe rear X2. The outer peripheral surface of the thick frame portion 34is positioned closer to the outer peripheral side than the outerperipheral surface of the thin frame portion 35 is, and between theseportions, an annular rearward surface 34 a is formed that extends alongthe radial direction R. On the outer peripheral surface of the thickframe portion 34, an external thread 36 is formed that can be threadedlyengaged with the internal thread 11 of the front ring 4. In the thinframe portion 35, an adhesive injection hole 37 is formed that passesthrough the thin frame portion in the radial direction R to be open onthe filter holding surface 33.

If an adhesive is injected from the outer peripheral side of the annularframe 31 through the adhesive injection hole 37 with the polarizationfilter 2 held to the filter holding surface 33, the adhesive enables thepolarization filter 2 to be fixed to the inner ring 3. The number ofadhesive injection holes 37 may be one, but a plurality of adhesiveinjection holes 37 are open on the thin frame portion 35 at equalangular intervals in the present embodiment.

The front stopper 32 is an annular protrusion that protrudes from thefront edge of the annular frame 31 toward the inner peripheral side. Thefront stopper 32 includes an annular rear end surface 32 a that is aflat surface orthogonal to the axis L. The front stopper 32 has a widthdimension from the annular rear end surface 32 a to the rear end of theannular frame 31 (width dimension W of the filter holding surface 33)larger than a thickness dimension D of the polarization filter 2 held bythe filter holding surface 33. The difference between the widthdimension W of the filter holding surface 33 in the fore-and-aftdirection X and the thickness dimension D of the polarization filter 2is 0.03 mm or less.

The inner ring 3 is inserted from the front side into the front ring 4with the polarization filter 2 held to the inner peripheral side of thefront annular frame 31. The external thread 36 of the inner ring 3 isthen threadedly engaged with the internal thread 11 of the front ring 4to be screwed until the rear end of the annular frame 31 abuts on therear annular wall portion 18 of the front ring 4. When the rear end ofthe annular frame 31 abuts on the rear annular wall portion 18, theannular rearward surface 34 a of the inner ring 3 faces the frontannular wall portion 16 of the front ring 4 in the fore-and-aftdirection X with a minute spacing allowed therebetween. The outerperipheral surface of the thin frame portion 35 of the annular frame 31also faces the intermediate annular plate portion 17 in the radialdirection R with a minute spacing therebetween. With the rear end of theannular frame 31 abutting on the rear annular wall portion 18, thedistance (width dimension W of the filter holding surface 33) betweenthe front stopper 32 and the rear annular wall portion 18 is larger thanthe thickness dimension D of the polarization filter 2. Consequently,the front ring 4 holds the polarization filter 2 rotatably about theaxis L between the front stopper 32 and the rear annular wall portion18. Specifically, the front stopper 32 and the rear annular wall portion18 do not grip the polarization filter 2 unrotatably. The polarizationfilter 2 is fixed to the inner ring 3 unrotatably by the adhesive. Therear annular wall portion 18 functions as a rear stopper that preventsthe polarization filter 2 from moving to the rear X2.

When the rear end of the annular frame 31 abuts on the rear annular wallportion 18 by screwing the inner ring 3 into the front ring 4, theannular rearward surface 34 a of the inner ring 3 may abut on the frontannular wall portion 16 of the front ring 4.

(Rear Ring)

The rear ring 5 includes a front annular plate portion 41 extending inthe fore-and-aft direction X along the axis L, an annular wall portion42 extending from the rear end of the front annular plate portion 41toward the inner peripheral side in the radial direction R, and a rearannular plate portion 43 extending from the inner peripheral end of theannular wall portion 42 to the rear X2 along the axis L. The frontannular plate portion 41 has a constant thickness dimension in theradial direction R. A grease holding recess 44 is formed on the frontend surface of the annular wall portion 42. The grease holding recess 44holds grease to slide the front ring 4 and the rear ring 5 smoothly. Theexternal thread 12 serving as a rear mounting portion is formed on theouter peripheral surface of the rear annular plate portion 43. Theannular protrusion 45 that protrudes toward the inner peripheral side inthe radial direction R is disposed on the inner peripheral surface ofthe rear annular plate portion 43.

The annular protrusion 45 includes a rectangular sectional shape. Theannular protrusion 45 has a width dimension in the fore-and-aftdirection X larger than the protrusion dimension to the inner peripheralside. The annular protrusion 45 is formed in a position overlapping theexternal thread 12 when seen from the radial direction R.

With the rear ring 5 holding the front ring 4, the front annular plateportion 41 is slidably fitted into the annular step 25 of the front ring4. This structure allows the outer peripheral surface 41 a of the frontannular plate portion 41 to be steplessly continuous to the outerperipheral surface 15 a of the thick portion 23 in the front annularplate portion 15 of the front ring 4. The annular wall portion 42 abutson the front annular wall portion 16 of the front ring 4 from the rearX2, while the rear annular plate portion 43 abuts on the intermediateannular plate portion 17 of the front ring 4 from the outer peripheralside. The annular protrusion 45 abuts on the rear annular wall portion18 of the front ring 4 from the rear X2. The inner peripheral portion ofthe annular protrusion 45 is inserted into the annular recess 21 on theouter peripheral surface of the inner ring 3. This structure allows therear ring 5 to hold the front ring 4 rotatably about the axis L.

(Assembly of Camera Filter Unit)

FIGS. 3A, 3B and 3C are diagrams for describing an assembling operationof the camera filter unit 1. In order to assemble the camera filter unit1, the front ring 4 and the rear ring 5 are first combined with eachother in the fore-and-aft direction X so that the position of theannular protrusion 45 of the rear ring 5 is between the rear annularwall portion 18 of the front ring 4 and the annular projection portion20 in the fore-and-aft direction X.

In the state before the front ring 4 and the rear ring 5 are combined,the rear annular plate portion 19 of the front ring 4 extends along theaxis L, as illustrated in FIG. 3A. Thus, the annular projection portion20 projects from the rear end of the rear annular plate portion 19 inthe radial direction R, and an outer peripheral end surface 20 a of theannular projection portion 20 extends parallel to the axis L. Theannular groove 27 includes a rectangular section. The notch 28 isnotched downward toward the rear X2 and has a triangular sectionalshape. When the front ring 4 and the rear ring 5 are disposed coaxially,the outer peripheral end surface 20 a of the annular projection portion20 of the front ring 4 is positioned flush with an inner peripheral endsurface 45 a of the annular protrusion 45 of the rear ring 5 orpositioned slightly closer to the inner peripheral side than the innerperipheral end surface 45 a is. Consequently, the front ring 4 and therear ring 5 are brought closer to each other while being maintainedcoaxially, whereby the annular protrusion 45 of the rear ring 5 can bepositioned between the rear annular wall portion 18 of the front ring 4and the annular projection portion 20.

As illustrated in FIG. 3B, the annular protrusion 45 of the rear ring 5is then caused to abut on the rear annular wall portion 18 of the frontring 4 from the rear X2. Subsequently, the rear annular plate portion 19of the front ring 4 is bent (plastically deformed) to the outerperipheral side to displace the annular projection portion 20 to theouter peripheral side. This structure creates the state in which theannular protrusion 45 of the rear ring 5 is inserted into the annularrecess 21 of the front ring 4.

When the rear annular plate portion 19 of the front ring 4 is bent tothe outer peripheral side, a force exerted from the inner peripheralside to the outer peripheral side in the radial direction R is appliedto the rear annular plate portion 19. As a result, the rear annularplate portion 19 is bent at the portion on the front end side thethickness of which is reduced by the formation of the annular groove 27,as illustrated in FIG. 3C. Additionally, the rear annular plate portion19 is bent to the outer peripheral side, whereby the annular projectionportion 20 projects to the outer peripheral side more than the innerperipheral end surface 45 a of the annular protrusion 45 does.Consequently, the state in which the annular protrusion 45 is insertedinto the annular recess 21 is created. The notch 28 serves as a reliefpart to avoid causing the rear annular plate portion 19 to abut on theannular protrusion 45 when the rear annular plate portion 19 is bent tothe outer peripheral side.

In the present embodiment, the portion the thickness of which is reducedby the formation of the annular groove 27 is provided to the front endof the rear annular plate portion 19 so as to bend the thin portion tothe outer peripheral side. Consequently, the rear annular plate portion19 can be bent accurately with relatively weak force. This enables theannular projection portion 20 to be displaced accurately to the outerperipheral side, improving the accuracy of dimension between the annularprotrusion 45 of the rear ring 5 and the annular recess 21 of the frontring 4. The annular projection portion 20 of the front ring 4 cantherefore be opposed to the annular protrusion 45 of the rear ring 5 atthe rear X2 with a minute spacing G that is set in advance allowedtherebetween. In the present embodiment, the spacing G can be between0.03 mm and 0.1 mm. Consequently, the front ring 4 can be prevented fromrattling on the rear ring 5 when the front ring 4 is rotated. The frontring 4 can also be rotated smoothly with respect to the rear ring 5.

Thereafter, the polarization filter 2 is inserted into the inner ring 3from the rear X2, causing the polarization filter 2 to abut on the frontstopper 32. Additionally, an adhesive is injected through the adhesiveinjection hole 37 to fix the polarization filter 2 to the inner ring 3.The inner ring 3 is then screwed into the front ring 4 from the frontX1, causing the rear end of the annular frame 31 of the inner ring 3 toabut on the rear annular wall portion 18 of the front ring 4. Thiscompletes the camera filter unit 1. In the state in which the camerafilter unit 1 is completed, the polarization filter 2 is held by thefront ring 4 between the front stopper 32 and the rear annular wallportion 18 in a rotatable manner about the axis L while being fixed tothe inner ring 3 unrotatably by the adhesive.

An adhesive may be applied to the annular rearward surface 34 a of theinner ring 3 or the front annular wall portion 16 of the front ring 4 inadvance to fix the inner ring 3 to the front ring 4 by the adhesive.

(Working Effect)

According to the present embodiment, the front ring 4 can rotate aboutthe axis L using the annular protrusion 45 of the rear ring 5 that isinserted into the annular recess 21 as a guide. Consequently, no washerneeds to be used to allow the rear ring 5 to hold the front ring 4rotatably. In the case in which the front ring 4 is rotated using theannular protrusion 45 that is disposed in the rear ring 5 as a guide,the guide (annular protrusion 45) does not become distorted, nor doesthe position of the guide (annular protrusion 45) change. The annularprotrusion 45 serving as a guide can be formed more accurately than awasher that expands and contracts in the radial direction, for example.Furthermore, because the present embodiment enables the annularprojection portion 20 to be displaced accurately to the outer peripheralside, the accuracy of dimension between the annular protrusion 45 of therear ring 5 and the annular recess 21 of the front ring 4 is high. Inaddition to this, because no member such as a washer is interposedbetween the front ring 4 and the rear ring 5, the front ring 4 and therear ring 5 can be combined accurately. The front ring 4 held by therear ring 5 can therefore be rotated smoothly.

The annular protrusion 45 of the rear ring 5 is disposed in a positionoverlapping the external thread 36 when seen from the radial directionR. Consequently, the dimension of the camera filter frame 10 can bereduced in the fore-and-aft direction X compared with the case in whichthe annular protrusion 45 is formed in a position different from that ofthe external thread 36 in the direction of the axis L.

Furthermore, the polarization filter 2 is held by the front ring 4between the front stopper 32 and the rear annular wall portion 18 in arotatable manner about the axis L, and is fixed to the inner ring 3unrotatably by the adhesive. Consequently, stress (pressure) to beplaced on the polarization filter 2 can be reduced compared with thecase in which the polarization filter 2 is held to the front ring 4 inan unrotatable manner while being gripped by the front stopper 32 andthe rear annular wall portion 18 (rear stopper) from the front and rear.Because distortion can be prevented from occurring in the polarizationfilter 2 with lower stress placed on the polarization filter 2, finerimages and videos can be obtained when, for example, images and videosthe resolution of which is many times higher than full high-definitionones are shot.

The adhesive injection hole 37 is formed in the inner ring 3 that isheld on the inner peripheral side of the front ring 4, which preventsthe adhesive injection hole 37 from being exposed to the outerperipheral side not to impair the appearance of the camera filter frame10.

The width dimension W of the filter holding surface 33 can be the sameas the thickness dimension D of the polarization filter 2, and astructure can also be employed in which the polarization filter 2 isgripped unrotatably between the front stopper 32 and the rear annularwall portion 18 when the rear end of the annular frame 31 is caused toabut on the rear annular wall portion 18.

Second Embodiment

FIG. 4A is a longitudinal sectional view of a camera filter unitaccording to a second embodiment. FIG. 4B is a partially enlargedsectional view thereof. As illustrated in FIG. 4A, a camera filter unit1A according to the present embodiment includes a disc-like polarizationfilter (optical element) 2, a front ring 4 for holding the polarizationfilter 2 coaxially, and a rear ring 5 for holding the front ring 4rotatably about the axis L. The camera filter unit 1A also includes afront stopper 6 that is attached to the inner peripheral surface of thefront ring 4 and restricts the movement of the polarization filter 2 tothe front X1. The front ring 4, the rear ring 5, and the front stopper 6constitute a camera filter frame 10A. Note that the camera filter unit1A according to the present embodiment includes components correspondingto those of the camera filter unit 1, and thus the same referencenumerals are given to the corresponding components for descriptionthereof.

As illustrated in FIG. 4A, on the inner peripheral surface of the frontring 4, an internal thread 11 is provided in a region of a certain widthfrom the front edge toward the rear X2. The front portion of theinternal thread 11 that is exposed to the front side more than the frontstopper 6 is a front mounting portion for mounting a cap or a hood intothe front of the camera filter unit 1A. On the outer peripheral surfaceof the rear ring 5, an external thread 36 is provided in a region of acertain width from the rear edge toward the front X1. The externalthread 36 is a rear mounting portion for mounting the camera filter unit1A into a lens-barrel of an imaging lens or a camera. The front stopper6, the front ring 4, and the rear ring 5 are all formed of a metal base.In the present embodiment, the front stopper 6, the front ring 4, andthe rear ring 5 are made of aluminum.

(Front Ring)

As illustrated in FIG. 4B, the front ring 4 includes a front annularplate portion 15 extending in the fore-and-aft direction X along theaxis L, an intermediate annular plate portion (holding portion) 17 thatis continuous to the rear end of the front annular plate portion 15 andextends on the inner peripheral side of the front annular wall portion15 to the rear X2 along the axis L, a rear annular wall portion (annularwall portion) 18 extending from the rear end of the intermediate annularplate portion 17 toward the inner peripheral side in the radialdirection R orthogonal to the axis L, a rear annular plate portion 19extending from the inner peripheral end of the rear annular wall portion18 to the rear X2, and an annular projection portion 20 projecting for ashorter distance than the rear annular wall portion 18 from the rear endof the rear annular plate portion 19 toward the outer peripheral side.On the outer peripheral surface of the front ring 4, an annular step 25is formed by the front annular wall portion 15 and the intermediateannular plate portion 17. On the outer peripheral surface of the frontring 4, an annular recess 21 is also formed by the rear annular wallportion 18, the rear annular plate portion 19, and the annularprojection portion 20.

The internal thread 11 serving as a front mounting portion is formed onthe inner peripheral surface of the front annular plate portion 15. Theintermediate annular plate portion 17 has a constant thickness in theradial direction R. The inner peripheral surface of the intermediateannular plate portion 17 (surface positioned between the front endsurface of the intermediate annular plate portion 17 and the front endsurface of the rear annular wall portion 18) is an annular surface thatextends with a constant diameter dimension along the axis L, and is afilter holding surface 17 a for holding the polarization filter 2coaxially. The filter holding surface 17 a has a width dimension Wlarger than a thickness dimension D of the polarization filter 2 held bythe filter holding surface 17 a. The difference between the widthdimension W of the filter holding surface 17 a and the thicknessdimension D of the polarization filter 2 is 0.03 mm or less.

The rear annular wall portion 18 has a constant thickness dimension inthe fore-and-aft direction X. The rear annular wall portion 18 functionsas a rear stopper that restricts the movement of the polarization filter2 that is held by the filter holding surface 17 a to the rear X2.

The rear annular plate portion 19 inclines to the outer peripheral sidetoward the rear X2. More specifically, the front end of the outerperipheral surface of the rear annular plate portion 19 (portionadjacent to the rear annular wall portion 18) is provided with anannular groove 27, and the portion in which the annular groove 27 isformed is bent to the outer peripheral side so that the rear annularplate portion 19 inclines to the outer peripheral side. The rear portionof the outer peripheral surface of the rear annular plate portion 19(portion adjacent to the annular projection portion 20) is provided withan annular notch 28. The notch 28 is shallower than the annular groove27.

The annular projection portion 20 projects in a direction orthogonal tothe rear annular plate portion 19. Consequently, the annular projectionportion 20 extends to the front X1 toward the outer peripheral side. Inthe present embodiment, the annular projection portion 20 has atrapezoidal sectional shape tapering toward the tip. The innerperipheral portion of an annular protrusion 45 of the rear ring 5 isinserted into the annular recess 21 formed by the rear annular wallportion 18, the rear annular plate portion 19, and the annularprojection portion 20.

(Front Stopper)

The front stopper 6 has a ring shape. The front stopper 6 has a heightdimension in the radial direction R larger than a height dimension ofthe intermediate annular plate portion 17 of the front ring in theradial direction R (thickness of the intermediate annular plate portion17). The front stopper 6 also includes an annular rear end surface 6 athat is a flat surface orthogonal to the axis L. On the entire outerperipheral surface of the front stopper 6, an external thread 51 isformed that can be threadedly engaged with the internal thread 11 of thefront ring 4. The external thread 51 of the front stopper 6 isthreadedly engaged with the internal thread 11 of the front ring 4 to bescrewed until the annular rear end surface 6 a of the front stopper 6abuts on the front end surface of the intermediate annular plate portion17. In the state in which the front stopper 6 abuts on the intermediateannular plate portion 17, the inner peripheral end of the front stopper6 projects to the inner peripheral side more than the filter holdingsurface 17 a does. Consequently, the front stopper 6 can restrict themovement of the polarization filter 2 that is held by the filter holdingsurface 17 a to the front X1.

(Rear Ring)

The front ring 4 includes a front annular plate portion (annularportion) 41 extending in the fore-and-aft direction X along the axis L,an annular wall portion 42 extending from the rear end of the frontannular plate portion 41 toward the inner peripheral side in the radialdirection R, and a rear annular plate portion 43 extending from theinner peripheral end of the annular wall portion 42 to the rear X2 alongthe axis L. The front annular plate portion 41 has a constant thicknessdimension in the radial direction R. A grease holding recess 44 isformed on the front end surface of the annular wall portion 42. Thegrease holding recess 44 holds grease to slide the front ring 4 and therear ring 5 smoothly. The external thread 12 serving as a rear mountingportion is formed on the outer peripheral surface of the rear annularplate portion 43.

The annular protrusion 45 that protrudes toward the inner peripheralside in the radial direction R is disposed on the front end of the innerperipheral surface of the rear annular plate portion 43. The annularprotrusion 45 includes a rectangular sectional shape. The front endsurface of the annular protrusion 45 is steplessly continuous to thefront end surface of the annular wall portion 42. The annular protrusion45 has a width dimension in the fore-and-aft direction X larger than theprotrusion dimension to the inner peripheral side. The annularprotrusion 45 is formed in a position partially overlapping the externalthread 12 when seen from the radial direction R.

With the rear ring 5 holding the front ring 4, the front annular plateportion 41 is fitted into the annular step 25 of the front ring 4 in africtionally movable manner. This structure allows the outer peripheralside 41 a of the front annular plate portion 41 to be steplesslycontinuous to the outer peripheral side 15 a of the front annular plateportion 15 of the front ring 4. The rear annular plate portion 43 abutson the rear end of the intermediate annular plate portion 17 of thefront ring 4 from the rear X2. The annular protrusion 45 abuts on therear end of the rear annular wall portion 18 of the front ring 4 fromthe rear X2. The inner peripheral portion of the annular protrusion 45is inserted into the annular recess 21 cut on the outer peripheralsurface of the front stopper 6. This structure allows the rear ring 5 tohold the front ring 4 rotatably about the axis L.

(Assembly of Camera Filter Unit)

In order to assemble the camera filter unit 1A, the front ring 4 and therear ring 5 are first combined with each other coaxially in thefore-and-aft direction X. The annular protrusion 45 of the rear ring 5is then inserted into the annular recess 21 on the outer peripheralsurface of the front ring 4. The assembling operation of insertingannular protrusion 45 of the rear ring 5 into the annular recess 21 onthe outer peripheral surface of the front ring 4 is the same as that forthe camera filter frame 10 according to the first embodiment. Thedescription thereof will thus be omitted.

Thereafter, the polarization filter 2 is inserted into the front ring 4from the front X1, causing the filter holding surface 17 a to hold thepolarization filter 2. The front stopper 6 is then screwed into thefront ring 4 from the front X1, causing the annular rear end surface 6 aof the front stopper 6 to abut on the intermediate annular plate portion17 of the front ring 4. This completes the camera filter unit 1A. In thestate in which the camera filter unit 1A is completed, the polarizationfilter 2 is held by the front ring 4 between the front stopper 6 and therear annular wall portion 18 in a rotatable manner about the axis L.

An adhesive may be applied to the annular rear end surface 6 a of thefront stopper 6 or the front end surface of the intermediate annularplate portion 17 of the front ring 4 in advance to fix the front stopper6 to the front ring 4 by the adhesive.

(Working Effect)

According to the present embodiment, the front ring 4 can rotate aboutthe axis L using the annular protrusion 45 of the rear ring 5 that isinserted into the annular recess 21 as a guide. Consequently, no washerneeds to be used to allow the rear ring 5 to hold the front ring 4rotatably. In the case in which the front ring 4 is rotated using theannular protrusion 45 that is disposed in the rear ring 5 as a guide,the guide (annular protrusion 45) does not become distorted, nor doesthe position of the guide (annular protrusion 45) change. The annularprotrusion 45 serving as a guide can be formed more accurately than awasher that expands and contracts in the radial direction, for example.Furthermore, because the present embodiment enables the annularprojection portion 20 to be displaced accurately to the outer peripheralside, the accuracy of dimension between the annular protrusion 45 of therear ring 5 and the annular recess 21 of the front ring 4 is high. Inaddition to this, because no member such as a washer is interposedbetween the front ring 4 and the rear ring 5, the front ring 4 and therear ring 5 can be combined accurately. The front ring 4 held by therear ring 5 can therefore be rotated smoothly.

Because the annular protrusion 45 of the rear ring 5 is disposed in aposition overlapping the external thread 51 when seen from the radialdirection R, the dimension of the camera filter frame 10A can be reducedin the fore-and-aft direction X compared with the case in which theannular protrusion 45 is formed in a position different from that of themounting portion in the direction of the axis L.

Furthermore, the front ring 4 holds the polarization filter 2 rotatablyabout the axis L between the front stopper 6 and the rear annular wallportion 18. Consequently, stress (pressure) to be placed on thepolarization filter 2 can be reduced compared with the case in which thepolarization filter 2 is gripped by the front stopper 6 and the rearannular wall portion 18 (rear stopper) from the front and rear to beunrotatable, which can prevent distortion from occurring in thepolarization filter 2.

As shown by the dotted lines in FIG. 4B, in the intermediate annularplate portion 17 of the front ring 4, an adhesive injection hole 37 canbe provided that passes through the intermediate annular plate portionin the direction intersecting the axis L to be open on the filterholding surface 17 a. In the case in which the adhesive injection hole37 is provided, the polarization filter 2 can be fixed to the front ring4 by injecting an adhesive through the adhesive injection hole 37. Theintermediate annular plate portion 17 is positioned on the innerperipheral side of the front annular plate portion 41 in the rear ring5. Consequently, even in the case in which the adhesive injection hole37 is formed in the intermediate annular plate portion 17, the adhesiveinjection hole 37 is not exposed to the outer peripheral side not toimpair the appearance of the camera filter frame 10.

The width dimension W of the filter holding surface 17 a can be the sameas the thickness dimension D of the polarization filter 2, and astructure can also be employed in which the polarization filter 2 isgripped unrotatably between the front stopper 6 and the rear annularwall portion 18.

Third Embodiment

FIG. 5A is a longitudinal sectional view of a camera filter unitaccording to a third embodiment. FIG. 5B is a partially enlargedsectional view thereof. A camera filter unit 1B according to the presentembodiment includes a disc-like polarization filter (optical element) 2,an inner ring 3 for holding the polarization filter 2 coaxially, a frontring 4 for holding the inner ring 3 coaxially from the outer peripheralside, and a rear ring 5 for holding the front ring 4 coaxially. Thecamera filter unit 1B according to the present embodiment also includesa disc-like second polarization filter (second optical element) 60, anda rear inner ring 61 that is inserted into the rear ring 5 from the rearto hold the second polarization filter 60 coaxially. The rear inner ring61 is made of aluminum.

The front ring 4 holds the polarization filter 2 via the inner ring 3.The rear ring 5 holds the second polarization filter 60 via the rearinner ring 61. The rear ring 5 also holds the front ring 4 rotatablyabout the axis L. The inner ring 3, the front ring 4, the rear ring 5,and the rear inner ring 61 constitute a camera filter frame 10B.

In the camera filter unit 1B according to the present embodiment, aholding structure for the polarization filter 2 in which the front ring4 holds the polarization filter 2 is the same as that in the camerafilter unit 1 according to the first embodiment. A holding structure forthe front ring 4 in which the rear ring 5 holds the front ring 4rotatably about the axis L is also the same as those in the camerafilter units 1 and 1A according to the first and the second embodiments,respectively. The following thus describes a holding structure in whichthe rear ring 5 holds the second polarization filter 60. The samereference numerals are given to components in common with those of thecamera filter unit 1 according to the first embodiment and descriptionthereof will be omitted. In the camera filter unit 1B according to thepresent embodiment, the holding structure for the polarization filter 2in which the front ring 4 holds the polarization filter 2 is the same asthe holding structure in the camera filter unit 1A according to thesecond embodiment.

As illustrated in FIGS. 5A and 5B, the rear ring 5 includes a secondannular projection portion (a second annular projection portion and asecond front stopper) 64 that projects to the inner peripheral sidecloser to the rear X2 than the front ring 4 does. The rear ring 5 alsoincludes a thick portion 65 and an internal thread 66 to the rear sideof the second annular projection portion 64. More specifically, a rearannular plate portion 43 of the rear ring 5 extends to the rear X2longer than those in the camera filter units 1 and 1A according to thefirst and the second embodiments do, and includes the second annularprojection portion 64, the thick portion 65, and the internal thread 66on the inner peripheral surface thereof.

The second annular projection portion 64 projects toward the innerperipheral side in the radial direction R in a position that isseparated from an annular protrusion 45 to the rear X2. The position ofan annular projection portion 20 of the front ring 4 is between theannular protrusion 45 and the second annular projection portion 64 inthe fore-and-aft direction X. The thick portion 65 extends from a midwayposition of the second annular projection portion 64 in the radialdirection R to the rear X2 with a constant thickness. The second annularprojection portion 64 includes a first annular rearward surface 64 a onthe outer peripheral side of the thick portion 65. The internal thread66 is provided continuously to the rear X2 of the thick portion 65. Thethick portion 65 includes a second annular rearward surface 65 a betweenthe thick portion 65 and the internal thread 66. An external thread 12serving as a rear mounting portion is provided on the outer peripheralsurface of the rear end of the rear ring 5 (outer peripheral surface ofthe rear end of the rear annular plate portion 43).

The rear inner ring 61 includes a rear annular frame 70 for holding thesecond polarization filter 60 coaxially from the outer peripheral side,and a second rear stopper (second rear stopper) 71 that projects fromthe rear edge of the rear annular frame 70 to the inner peripheral sideto restrict the movement of the second polarization filter 60 to therear X2. The second rear stopper 71 is abuttable from the rear X2 on theouter peripheral edge of the second polarization filter 60 that is heldby the rear annular frame 70. The inner peripheral surface of the rearannular frame 70 is an annular surface that extends with a constantdiameter dimension along the axis L, and is a rear filter holdingsurface 72 for holding the second polarization filter 60 coaxially.

The rear inner ring 61 includes a thin ring portion 73 and a thick ringportion 74 in this order from the front X1 toward the rear X2. The outerperipheral surface of the thick ring portion 74 is positioned closer tothe outer peripheral side than the outer peripheral surface of the thinring portion 73 is, and between these portions, an annular forwardsurface 74 a is formed that extends along the radial direction R. On theouter peripheral surface of the thick ring portion 74, an externalthread 75 is formed that can be threadedly engaged with the internalthread 66 of the rear ring 5. In the thin ring portion 73, a rearadhesive injection hole 76 is formed that passes through the thin ringportion in the radial direction R to be open on the rear filter holdingsurface 72. If an adhesive is injected from the outer peripheral side ofthe rear annular frame 70 through the rear adhesive injection hole 76with the second polarization filter 60 held to the rear filter holdingsurface 72, the adhesive enables the second polarization filter 60 to befixed to the rear inner ring 61. The number of rear adhesive injectionholes 76 may be one, but a plurality of rear adhesive injection holes 76are open on the thin ring portion 73 at equal angular intervals in thepresent embodiment. The rear adhesive injection hole 76 may also beomitted.

The second rear stopper 71 is an annular protrusion that protrudes fromthe rear edge of the rear annular frame 70 toward the inner peripheralside. The second rear stopper 71 includes an annular front end surface71 a that is a flat surface orthogonal to the axis L. The second rearstopper 71 has a width dimension from the annular front end surface 71 ato a front end 70 a of the rear annular frame 70 (width dimension of therear filter holding surface 72) W2 larger than a thickness dimension D2of the second polarization filter 60 held by the filter holding surface33. The difference between the width dimension W2 of the rear filterholding surface 72 in the fore-and-aft direction X and the thicknessdimension D2 of the second polarization filter 60 is 0.03 mm or less.

The rear inner ring 61 is inserted from the rear side into the rear ring5 with the second polarization filter 60 held to the inner peripheralside of the rear annular frame 70. The external thread 75 of the rearinner ring 61 is then threadedly engaged with the internal thread 66 ofthe rear ring 5 to be screwed until the front end 70 a of the rearannular frame 70 abuts on the second annular projection portion 64(first annular rearward surface 64 a) of the rear ring 5. When the frontend 70 a of the rear annular frame 70 abuts on the second annularprojection portion 64, the annular forward surface 74 a of the rearinner ring 61 faces the second annular rearward surface 65 a of the rearring 5 in the fore-and-aft direction X with a minute spacing allowedtherebetween. The outer peripheral surface of the thin ring portion 73of the rear annular frame 70 also faces the thick portion 65 of the rearring 5 in the radial direction R with a minute spacing allowedtherebetween.

With the front end 70 a of the rear annular frame 70 abutting on thesecond annular projection portion 64, the distance (width dimension ofthe rear filter holding surface 72) W2 between the second rear stopper71 and the second annular projection portion 64 is larger than thethickness dimension D2 of the second polarization filter 60.Consequently, the rear ring 5 holds the second polarization filter 60rotatably about the axis L between the second rear stopper 71 and thesecond annular projection portion 64. Specifically, the second rearstopper 71 and the second annular projection portion 64 do not grip thesecond polarization filter 60 unrotatably. The second polarizationfilter 60 is fixed to the rear inner ring 61 unrotatably by theadhesive. The second annular projection portion 64 functions as a secondfront stopper that prevents the second polarization filter 60 frommoving to the front X1.

When the front end 70 a of the rear annular frame 70 abuts on the secondannular projection portion 64 of the rear ring 5 by screwing the rearinner ring 61 into the rear ring 5, the annular forward surface 74 a ofthe rear inner ring 61 may abut on the second annular rearward surface65 a of the rear ring 5.

(Working Effect)

Also in the present embodiment, the working effect similar to the camerafilter units 1 and 1A according to the first and the second embodimentscan be obtained. In the present embodiment, the second polarizationfilter 60 is also held to the rear ring 5. In the present embodiment,two optical filters (the polarization filter 2 and the secondpolarization filter 60) can thus be held in the camera filter frame 10B.Furthermore, the rear ring 5 holds the second polarization filter 60rotatably about the axis L between the second rear stopper 71 and thesecond annular projection portion 64. Consequently, stress (pressure) tobe placed on the second polarization filter 60 can be reduced comparedwith the case in which the second polarization filter 60 is gripped bythe second rear stopper 71 and the second annular projection portion 64from the front and rear to be unrotatable. Therefore, distortion can beprevented from occurring in the second polarization filter 60.

The rear adhesive injection hole 76 is formed in the rear inner ring 61that is held on the inner peripheral side of the rear ring 5, whichprevents the rear adhesive injection hole 76 from being exposed to theouter peripheral side not to impair the appearance of the camera filterframe 10B.

The width dimension W2 of the rear filter holding surface 72 can be thesame as the thickness dimension D2 of the second polarization filter 60,and a structure can also be employed in which the second polarizationfilter 60 is gripped unrotatably between the second rear stopper 71 andthe second annular projection portion 64.

The internal thread 66 of the rear ring 5 and the external thread 75 ofthe rear inner ring 61 may be omitted and the rear inner ring 61 may befixed to the inner peripheral side of the rear ring 5 by the adhesive.

Furthermore, the optical elements held by the front ring 4 and the rearring 5 are not limited to polarization filters. For example, apolarization filter can be held to the front ring 4 and a color filtercan be held to the rear ring 5. Alternatively, for example, a crossfilter can be held to the front ring 4 and a color filter can be held tothe rear ring 5.

Fourth Embodiment

FIG. 6A is a longitudinal sectional view of a camera filter unitaccording to a fourth embodiment. FIG. 6B is a partially enlargedsectional view thereof. A camera filter unit 1C according to the presentembodiment includes a disc-like polarization filter (optical element) 2,an inner ring 3 for holding the polarization filter 2 coaxially, a frontring 4 for holding the inner ring 3 coaxially from the outer peripheralside, and a rear ring 5 for holding the front ring 4 coaxially. Thecamera filter unit 1C according to the present embodiment also includesa disc-like second polarization filter (second optical element) 60, anda rear inner ring 81 that is inserted into the rear ring 5 from the rearX2 to hold the second polarization filter 60 coaxially. The rear innerring 81 is made of aluminum.

The front ring 4 holds the polarization filter 2 via the inner ring 3.The rear ring 5 holds the second polarization filter 60 via the rearinner ring 81. The rear ring 5 also holds the front ring 4 rotatablyabout the axis L. The inner ring 3, the front ring 4, the rear ring 5,and the rear inner ring 81 constitute a camera filter frame 10C.

In the camera filter unit 1C according to the present embodiment, aholding structure for the polarization filter 2 in which the front ring4 holds the polarization filter 2 is the same as that in the camerafilter unit 1 according to the first embodiment. A holding structure forthe front ring 4 in which the rear ring 5 holds the front ring 4rotatably about the axis L is also the same as those in the camerafilter units 1 and 1A according to the first and the second embodiments,respectively. The following thus describes a holding structure in whichthe rear ring 5 holds the second polarization filter 60. The samereference numerals are given to components in common with those of thecamera filter unit 1 according to the first embodiment and descriptionthereof will be omitted. In the camera filter unit 1C according to thepresent embodiment, the holding structure for the polarization filter 2in which the front ring 4 holds the polarization filter 2 is the same asthe holding structure in the camera filter unit 1A according to thesecond embodiment.

As illustrated in FIGS. 6A and 6B, the rear ring 5 includes a secondannular projection portion (a second annular projection portion and asecond front stopper) 84 that projects to the inner peripheral sidecloser to the rear X2 than the front ring 4 does. The rear ring 5 alsoincludes an internal thread 85 to the rear side of the second annularprojection portion 84. More specifically, a rear annular plate portion43 of the rear ring 5 extends to the rear X2 longer than those in thecamera filter units 1 and 1A according to the first and the secondembodiments do, and includes the second annular projection portion 84and the internal thread 85 on the inner peripheral surface thereof.

The second annular projection portion 84 projects toward the innerperipheral side in the radial direction R in a position that isseparated from an annular protrusion 45 to the rear X2. The position ofan annular projection portion 20 of the front ring 4 is between theannular protrusion 45 and the second annular projection portion 84 inthe fore-and-aft direction X. The internal thread 85 is providedcontinuously to the rear X2 of the second annular projection portion 84.The second annular projection portion 84 includes an annular rearwardsurface 84 a between the second annular projection portion 84 and theinternal thread 85. An external thread 12 serving as a rear mountingportion is provided on the outer peripheral surface of the rear end ofthe rear ring 5 (outer peripheral surface of the rear end of the rearannular plate portion 43).

The rear inner ring 81 includes a rear annular frame 86 for holding thesecond polarization filter 60 coaxially from the outer peripheral side,and a second rear stopper (second rear stopper) 87 that projects fromthe rear edge of the rear annular frame 86 to the inner peripheral sideto restrict the movement of the second polarization filter 60 to therear X2. The second rear stopper 87 is abuttable from the rear X2 on theouter peripheral edge of the second polarization filter 60 that is heldby the rear annular frame 86. The inner peripheral surface of the rearannular frame 86 is an annular surface that extends with a constantdiameter dimension along the axis L, and is a rear filter holdingsurface 88 for holding the second polarization filter 60 coaxially. Onthe outer peripheral surface of the rear inner ring 81, an externalthread 89 is formed that can be threadedly engaged with the internalthread 85 of the rear ring 5.

In the rear annular frame 86, a rear adhesive injection hole 90 isformed that passes through the rear annular frame in the radialdirection R to be open on the rear filter holding surface 88. If anadhesive is injected from the outer peripheral side of the rear annularframe 86 through the rear adhesive injection hole 90 with the secondpolarization filter 60 held to the rear filter holding surface 88, theadhesive enables the second polarization filter 60 to be fixed to therear inner ring 81. The number of rear adhesive injection holes 90 maybe one, but a plurality of rear adhesive injection holes 90 are open onthe thin ring portion 73 at equal angular intervals in the presentembodiment. The rear adhesive injection hole 90 may also be omitted.

The second rear stopper 87 is an annular protrusion that protrudes fromthe rear edge of the rear annular frame 86 toward the inner peripheralside. The second rear stopper 87 includes an annular front end surface87 a that is a flat surface orthogonal to the axis L. The second rearstopper 87 has a width dimension from the annular front end surface 87 ato a front end 86 a of the rear annular frame 86 (width dimension of therear filter holding surface 88) W2 larger than a thickness dimension D2of the second polarization filter 60 held by the filter holding surface33. The difference between the width dimension W2 of the rear filterholding surface 88 in the fore-and-aft direction X and the thicknessdimension D2 of the second polarization filter 60 is 0.03 mm or less.

The rear inner ring 81 is inserted from the rear side into the rear ring5 with the second polarization filter 60 held to the inner peripheralside of the rear annular frame 86. The external thread 89 of the rearinner ring 81 is then threadedly engaged with the internal thread 85 ofthe rear ring 5 to be screwed until the front end 86 a of the rearannular frame 86 abuts on the second annular projection portion 84(annular rearward surface 84 a) of the rear ring 5.

With the front end 86 a of the rear annular frame 86 abutting on thesecond annular projection portion 84, the distance (width dimension ofthe rear filter holding surface 95) W2 between the second rear stopper87 and the second annular projection portion 84 is larger than thethickness dimension D2 of the second polarization filter 60.Consequently, the rear ring 5 holds the second polarization filter 60rotatably about the axis L between the second rear stopper 87 and thesecond annular projection portion 84. Specifically, the second rearstopper 87 and the second annular projection portion 84 do not grip thesecond polarization filter 60 unrotatably. The second polarizationfilter 60 is fixed to the rear inner ring 81 unrotatably by theadhesive. The second annular projection portion 84 functions as a secondfront stopper that prevents the second polarization filter 60 frommoving to the front X1.

(Working Effect)

Also in the present embodiment, the working effect similar to the camerafilter units 1 and 1A according to the first and the second embodimentscan be obtained. In the present embodiment, the second polarizationfilter 60 is also held to the rear ring 5. Specifically, two opticalfilters can be held in the camera filter frame 10C in the presentembodiment. Furthermore, the rear ring 5 holds the second polarizationfilter 60 rotatably about the axis L between the second rear stopper 87and the second annular projection portion 84. Consequently, stress(pressure) to be placed on the second polarization filter 60 can bereduced compared with the case in which the second polarization filter60 is gripped by the second rear stopper 87 and the second annularprojection portion 84 from the front and rear to be unrotatable.Therefore, distortion can be prevented from occurring in the secondpolarization filter 60.

The rear adhesive injection hole 90 is formed in the rear inner ring 81that is held on the inner peripheral side of the rear ring 5, whichprevents the rear adhesive injection hole 90 from being exposed to theouter peripheral side not to impair the appearance of the camera filterframe 10C.

The width dimension W2 of the rear filter holding surface 88 can be thesame as the thickness dimension D2 of the second polarization filter 60,and a structure can also be employed in which the second polarizationfilter 60 is gripped unrotatably between the second rear stopper 87 andthe second annular projection portion 84. The rear inner ring 81 may befixed to the inner peripheral side of the rear ring 5 by the adhesive.Furthermore, the optical elements held by the front ring 4 and the rearring 5 are not limited to polarization filters.

Fifth Embodiment

FIG. 7A is a longitudinal sectional view of a camera filter unitaccording to a fifth embodiment. FIG. 7B is a partially enlargedsectional view thereof. A camera filter unit 1D according to the presentembodiment includes a disc-like polarization filter (optical element) 2,an inner ring 3 for holding the polarization filter 2 coaxially, a frontring 4 for holding the inner ring 3 coaxially from the outer peripheralside, and a rear ring 5 for holding the front ring 4 coaxially. Thecamera filter unit 1D according to the present embodiment also includesa disc-like second polarization filter (second optical element) 60, anda second rear stopper 91 that is inserted into the rear ring 5 from therear X2 to restrict the movement of the second polarization filter 60 tothe rear X2. The second rear stopper 91 is made of aluminum.

The front ring 4 holds the polarization filter 2 via the inner ring 3.The rear ring 5 holds the second polarization filter 60. The rear ring 5also holds the front ring 4 rotatably about the axis L. The inner ring3, the front ring 4, the rear ring 5, and the second rear stopper 91constitute a camera filter frame 10D.

In the camera filter unit 1D according to the present embodiment, aholding structure for the polarization filter 2 in which the front ring4 holds the polarization filter 2 is the same as that in the camerafilter unit 1 according to the first embodiment. A holding structure forthe front ring 4 in which the rear ring 5 holds the front ring 4rotatably about the axis L is also the same as those in the camerafilter units 1 and 1A according to the first and the second embodiments,respectively. The following thus describes a holding structure in whichthe rear ring 5 holds the second polarization filter 60. The samereference numerals are given to components in common with those of thecamera filter unit 1 according to the first embodiment and descriptionthereof will be omitted. In the camera filter unit 1D according to thepresent embodiment, the holding structure for the polarization filter 2in which the front ring 4 holds the polarization filter 2 is the same asthe holding structure in the camera filter unit 1A according to thesecond embodiment.

As illustrated in FIGS. 7A and 7B, the rear ring 5 includes a secondannular projection portion (a second annular projection portion and asecond front stopper) 92 that projects to the inner peripheral sidecloser to the rear X2 than the front ring 4 does. The rear ring 5 alsoincludes a thick portion 93 and an internal thread 94 to the rear sideof the second annular projection portion 92. More specifically, a rearannular plate portion 43 of the rear ring 5 extends to the rear X2longer than those in the camera filter units 1 and 1A according to thefirst and the second embodiments do, and includes the second annularprojection portion 92, the thick portion 93, and the internal thread 94on the inner peripheral surface thereof.

The second annular projection portion 92 projects toward the innerperipheral side in the radial direction R in a position that isseparated from an annular protrusion 45 to the rear X2. The position ofan annular projection portion 20 of the front ring 4 is between theannular protrusion 45 and the second annular projection portion 92 inthe fore-and-aft direction X. The thick portion 93 extends from a midwayposition of the second annular projection portion 92 in the radialdirection R to the rear X2 with a constant thickness. The second annularprojection portion 92 includes a first annular rearward surface 92 a onthe outer peripheral side of the thick portion 93.

The thick portion 93 is a rear holding portion for holding the secondpolarization filter 60 coaxially from the outer peripheral side.Specifically, the inner peripheral surface of the thick portion 93 is anannular surface that extends with a constant diameter dimension alongthe axis L, and is a rear filter holding surface 95 for holding thesecond polarization filter 60 coaxially. The rear filter holding surface95 has a width dimension W2 larger than a thickness dimension D2 of thesecond polarization filter 60 held by the rear filter holding surface95. The difference between the width dimension W2 of the rear filterholding surface 95 and the thickness dimension D2 of the secondpolarization filter 60 is 0.03 mm or less.

The internal thread 94 is provided continuously to the rear X2 of thethick portion 93. The thick portion 93 includes a second annularrearward surface 93 a between the thick portion 93 and the internalthread 94. An external thread 12 serving as a rear mounting portion isprovided on the outer peripheral surface of the rear end of the rearring 5 (outer peripheral surface of the rear end of the rear annularplate portion 43).

The second rear stopper 91 has a ring shape. The second rear stopper 91has a height dimension in the radial direction R larger than a heightdimension of the thick portion 93 of the rear ring 5 in the radialdirection R (thickness of the thick portion 93). The second rear stopper91 also includes an annular front end surface 91 a that is a flatsurface orthogonal to the axis L. On the entire outer peripheral surfaceof the second rear stopper 91, an external thread 96 is formed that canbe threadedly engaged with the internal thread 94 of the rear ring 5.The external thread 96 of the second rear stopper 91 is threadedlyengaged with the internal thread 94 of the rear ring 5 to be screweduntil the annular front end surface 91 a of the second rear stopper 91abuts on the second annular rearward surface 93 a of the thick portion93. In the state in which the second rear stopper 91 abuts on the thickportion 93, the inner peripheral end of the second rear stopper 91projects to the inner peripheral side more than the rear filter holdingsurface 95 does. Consequently, the second rear stopper 91 can restrictthe movement of the second polarization filter 60 that is held by therear filter holding surface 95 to the rear X2.

In order for the rear ring 5 to hold the second polarization filter 60,the second polarization filter 60 is first inserted into the rear ring 5from the rear X2 to cause the rear filter holding surface 95 to hold thesecond polarization filter 60. The second rear stopper 91 is thenscrewed into the rear ring 5 from the rear X2 to cause the annular frontend surface 91 a of the second rear stopper 91 to abut on the secondannular rearward surface 93 a of the thick portion 93. This completesthe camera filter unit 1D. In the state in which the camera filter unit1D is completed, the second polarization filter 60 is held by the rearring 5 between the second rear stopper 91 and the second annularprojection portion 92 in a rotatable manner about the axis L. The secondannular projection portion 92 functions as a second front stopper thatprevents the second polarization filter 60 from moving to the front X1.

(Working Effect)

Also in the present embodiment, the working effect similar to the camerafilter units 1 and 1A according to the first and the second embodimentscan be obtained. In the present embodiment, the second polarizationfilter 60 is also held to the rear ring 5. Specifically, two opticalfilters can be held in the camera filter frame 10C in the presentembodiment. Furthermore, the rear ring 5 holds the second polarizationfilter 60 rotatably about the axis L between the second rear stopper 91and the second annular projection portion 92. Consequently, stress(pressure) to be placed on the second polarization filter 60 can bereduced compared with the case in which the second polarization filter60 is gripped by the second rear stopper 91 and the second annularprojection portion 92 from the front and rear to be unrotatable.Therefore, distortion can be prevented from occurring in the secondpolarization filter 60.

The width dimension W2 of the rear filter holding surface 95 can be thesame as the thickness dimension D2 of the second polarization filter 60,and a structure can also be employed in which the second polarizationfilter 60 is gripped unrotatably between the second rear stopper 91 andthe second annular projection portion 92. The second rear stopper 91 maybe fixed to the inner peripheral side of the rear ring 5 by theadhesive. Furthermore, the optical elements held by the front ring 4 andthe rear ring 5 are not limited to polarization filters.

Other Embodiments

Although the annular groove 27 is cut on the outer peripheral surface ofthe rear annular plate portion 19 of the front ring 4 in the aboveembodiment, an annular groove may be cut on the inner peripheral surfaceof the rear annular plate portion 19, and the rear annular plate portion19 may be bent from the position in which the annular groove is formedto the outer peripheral side. Alternatively, annular grooves may be cutin respective positions on the inner peripheral surface and the outerperipheral surface of the rear annular plate portion 19 overlapping witheach other when seen from the radial direction R, and the rear annularplate portion 19 may be bent from the positions in which the annulargrooves are formed to the outer peripheral side. Furthermore, theannular groove 27 and the notch 28 may be omitted.

A cross filter can also be held to the front ring 4 as an opticalelement. Furthermore, a color filter may be held to the front ring 4 anda polarization filter or a cross filter may be held to the rear ring 5.Alternatively, a color filter may be held to each of the front ring 4and the rear ring 5.

1.-15. (canceled)
 16. A camera filter frame comprising: a ring having anannular projection portion, which project toward an inner peripheralside; an inner ring, which is held in the inner peripheral side of thering; wherein the inner ring has an annular frame for holding an opticalelement on the inner peripheral side, and a rear stopper, which projectsfrom a rear end of the annular frame toward the inner peripheral sidethereof and restricts a rearward movement of the optical element,wherein an inner peripheral surface of the annular frame which extendsfrom a front end thereof to the rear stopper thereof functions as aholding surface, which holds the optical element coaxially, the frontend of the annular frame is in contact with the annular projectionportion of the ring, and the annular projection portion is abuttablewith the optical element from a front side thereof.
 17. The camerafilter frame according to claim 16, wherein a distance between theannular projection portion and the rear stopper is longer than athickness of the optical element, and the optical element is held in arotatable manner about an axis.
 18. The camera filter frame according toclaim 17, further including an adhesive for fixing the optical elementto the holding surface so as not be rotatable thereinside, and a holefor adhesive injection, which passes through the annular frame from anouter peripheral side thereof to the holding surface thereof, whereinthe adhesive is filled the hole.
 19. The camera filter frame accordingto claim 16, wherein the ring has an internal thread on a rear side ofthe annular projection portion, and the inner ring has an externalthread on an outer peripheral surface thereof, which is screwed into aninternal thread.
 20. The camera filter frame according to claim 16,wherein the inner ring and the ring are fixed to each other by anadhesive.
 21. The camera filter frame according to claim 19, wherein thering has a thick portion, which extends rearward with a constantthickness from a midway position of the annular projection portion in aradial direction, the internal thread is provided on a rear side of thethick portion, the thick portion of the ring has an annular rearwardsurface between the thick portion thereof and the internal threadthereof, the inner ring has a thin ring portion and a thick ring portionin this order toward a rear thereof from a front thereof, the externalthread of the inner ring is formed on an outer peripheral surface of thethick ring portion thereof so that an outer peripheral surface of thethick ring portion is positioned so as to be closer to the outerperipheral side than an outer peripheral surface of the thin ringportion, the inner ring has an annular forward surface, which isdirected to the front, and provided between the thin ring portion andthe thick ring portion, and the annular forward surface of the innerring and the annular rearward surface of the ring face each other with agap, or are contact with each other.
 22. A camera filter unitcomprising: the camera filter frame according to claim 16; and anoptical element held in the camera filter frame.